The following steps reproduce the behaviour filed in the bug report



1. Start with an empty Authz file:

As verified / shown in: screenshot000

2. Add a new group, named: new_group
- then click the "Add" button

As shown in: screenshot001


3. Expand the group you just added, new_group. Do this by navigating to 
"Subversion Groups" section with "Manage Subversion Access Rights" and clicking
 on the group you just added.
4. Once the group is expanded click on the checkbox next to new_group
5. Click on "Remove selected groups"

see: screenshot002

6. The auth file should again be empty

see: screenshot003

7. Add a new path via the "Add Path:" dialog. Name the path: /new_path
- then click the "Add" button

see: screenshot004

8.  Expand the path you just added, new_path. Do this by navigating to
 "Subversion Paths" section with "Manage Subversion Access Rights" and clicking
 on the path you just added.
9. Once the path is expanded click on the checkbox next to *:/new_path
10. Click on "Remove selected paths"


see: screenshot005

11. An error message screen shows up

see: screenshot006

12. Navigate back to the SvnAuthzAdminPlugin plugin webpage in the Trac Administration panel:

see: screenshot007, screenshot008

13. Upon arriving at plugin webpage, the path just added remains.

see: screenshot009


Conclusion:
* A group listed under "Subversion Groups" when it is expanded (by clicking on it): *CAN* be removed (see screenshot002-003>)
* A  path listed under "Subversion Groups" when it is expanded (by clicking on it): *CANNOT* be removed (see screenshot005->006)